SUMMARY Our initial grant funding focused on the earliest period following experimentally-induced seizures. We documented robust physical interactions between microglia and neurons in epileptic contexts and concluded that microglia provide beneficial functions in the acute seizures. In this renewal, we will further investigate microglial activities in the epileptic brain in vivo and combine cellular and functional imaging with electrophysiological and behavioral studies in experimental mouse seizure models. We will extend our findings from the initial funding cycle to further characterize microglial activities in the epileptic brain following seizures and provide further evidence of microglial neuroprotection in the acute phase of kainic acid (KA)-induced seizures. In addition, we will investigate microglial roles in the epileptic brain in the chronic phase of epilepsy using microglial ablation and chemogenetic DREADD approaches. Our central hypothesis is that microglia play opposing roles during the acute phase of seizures and the chronic phase of epileptogenesis. This hypothesis will be tested along the following specific aims: In Aim 1, we will investigate the dynamics and function of seizure-induced microglial process pouches. In Aim 2, we will determine microglial contributions to epileptogenesis. Finally, in Aim 3, we will ascertain opposing microglial roles in acute seizures and chronic epilepsy using DREADD approaches. When completed, this grant will extend the findings of the initial funding to elucidate the beneficial roles for microglia in the acute phase of seizures Furthermore, this renewal will highlight detrimental contributions by microglia in promoting seizure-induced neurogenesis, neuronal sprouting, neuronal excitability and spontaneous seizures in the chronic phase of seizures. This study will not only improve our understanding of microglial mechanism to epileptogenesis but also demonstrate that microglia are potential therapeutic targets for the treatment seizures and epilepsy.